Abstract:
The W.M. Keck Foundation has awarded Rice University $1.4 million to probeone of the most elusive and mysterious areas of modern physics ­ the bizarreworld of high-temperature superconductors, quantum magnets, and othersolid-state materials that have "strongly correlated" electrons. Rice'sprogram will bring together theorists and experimentalists specializing inboth ultracold atomic matter and nanoscale condensed-matter physics.

Keck gives Rice $1.4M to probe quantum matter

HOUSTON, TX | Posted on February 12th, 2007

The W.M. Keck Foundation has awarded RiceUniversity $1.4 million to probe one of the most elusive and mysteriousareas of modern physics ­ the bizarre world of high-temperaturesuperconductors, quantum magnets, and other solid-state materials that have"strongly correlated" electrons.

"The past decade has witnessed incredible experimental breakthroughs in bothultracold atomic physics and condensed matter physics," said physicist RandyHulet, co-director of Rice's Keck Program in Quantum Materials. "We believeRice has all the pieces in place to make breakthroughs in our understandingof effects that have puzzled physicists for more than 20 years."

Given the past decade's advances in nanoscale fabrication, laser cooling andother technologies, many believe the stage is set for a major leap in ourunderstanding of exotic materials, such as high-temperature superconductors,where the electrons interact so strongly with one another that their actionscannot be explained by simple theories.

Unlike electrons in simple metals, which hardly notice one another, theelectrons in high-temperature superconductors and some magnetic materialsare intricately linked. Physicists cannot predict how any single electron inthe material will act without considering the actions of all of itsneighbors. While considerable theoretical efforts have been made, leading tothe development of major new concepts, a unified framework remains elusivefor the understanding of these strongly correlated electronic materials.

"It's the electron-electron interactions and quantum fluctuations in theseclasses of materials that both create these great effects and make them sodifficult to explain," said program co-director Doug Natelson, a condensedmatter experimentalist. "In most solid-state materials, physicists can oftenget away with ignoring interaction effects because they are overpowered bystronger forces. That's just not possible in these materials." Natelson saidtunable models of these materials based on either nanostructures or coldatoms can examine these issues directly.

For example, the advent of laser-cooling technology within the past decadehas allowed physicists working at the atomic scale to create a number ofelusive states of quantum matter, including Bose-Einstein Condensates, orBECs, which were first predicted by Albert Einstein in the 1920s. Under thenew Keck program, Hulet's lab ­ one of the first in the world to make BECs ­is preparing a new apparatus to test the two-dimensional Hubbard model, atheory put forward more than 20 years ago to describe the conduction andmagnetic properties of one type of strongly interacting materials, thehigh-temperature superconductors. Hulet said his apparatus will allow theuse of a gas of ultracold atoms in place of the electrons in real materialsto fine tune certain properties of the system and provide theorists withdata that they couldn't otherwise get from a real material.

Similarly, mobile electrons in ³heavy fermion² materials act hundreds oftimes more massive than those in ordinary metals because of quantuminteractions with magnetic atoms. The magnetic atoms also talk to eachother. A new experiment in Natelson¹s lab will use a single-moleculeelectronic device as a model of these rich materials. Dialing a voltage onthe device will controllably shift the relative importance of theinteractions, so that the system may be tuned from a normal metal state intoa quantum regime with unusual conducting properties. Studies of this quantumphase transition in real materials have given rise to many open questions,which the model system is uniquely suited to address.

These projects are two of several that the Keck Program will support. Inall, eight principle investigators at Rice will participate in the program.These include condensed matter experimentalists Jun Kono and Rui-Rui Du, andultracold atom experimentalist Tom Killian. Theoretical connections will bemade by atomic matter theorist Han Pu and condensed matter theorists QimiaoSi and Carl Bolech.

"Quantum magnetism and strong correlations are subjects in which theory andexperiment have always gone hand in hand over the course of studying realcondensed matter materials," said Si. "In the Keck program, theory will notonly provide the intellectual foundation but will also serve as theintellectual glue."

Hulet and Natelson said Rice is matching Keck's contribution with $1.4million of its own. They said the lion's share of program funds will pay thesalaries of three Keck Postdoctoral Fellows and three graduate students whowill focus exclusively on the program's projects.

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About Rice UniversityRice University is consistently ranked one of America’s best teaching andresearch universities. It is distinguished by its: size—2,850 undergraduatesand 1,950 graduate students; selectivity—10 applicants for each place in thefreshman class; resources—an undergraduate student-to-faculty ratio of 6-to-1, and the fifth largest endowment per student among American universities; residential college system, which builds communities that are both close-knit and diverse; and collaborative culture, which crosses disciplines, integrates teaching and research, and intermingles undergraduate and graduate work. Rice’s wooded campus is located in the nation’s fourth largest city and on America’s South Coast.